Reduction of Contact Resistance on Titanium Sheet Surfaces by Formation of Titanium Carbide and Nitride, and its Stability in Sulfuric Acid Aqueous Solution

Abstract

Separators for solid polymer fuel cells must have a low contact resistance with the carbon paper and stability in a corrosive environment of sulfuric acid in the cell. The titanium surface is highly resistant to corrosion thanks to a passive film but has high contact resistance. In this study, titanium carbide or nitride as the electrical conductor was formed on the surface by annealing commercially pure titanium sheet. The contact resistances of these sheets were evaluated before and after a sulfuric acid aqueous solution exposure test, "with a pH of 4 at 80°C for 4 days", briefly simulating the operating environment. In addition, the same evaluation test was conducted with a surface with TiC formed dipped in nitric acid to enhance the stability in a sulfuric acid solution. The initial contact resistance falls below 10 mΩ•cm 2 by formation of TiC and TiN, Ti 2 N on sheet surface. However, the contact resistance rises to 100 or above after the exposure test because a large amount of TiO 2 precipitates. This is probably because TiC and TiN are dissolved by sulfuric acid, generating TiO 2. By contrast, dipping in nitric acid hardly raises the contact resistance from less than 10 even after the exposure test. It is considered from the results of surface analyses that Ti ion generated by partial dissolution of TiC is turned into TiO 2 by the oxidizability of nitric acid, changing the surface structure covering TiC. It is considered that the newly formed TiO 2 film enhanced stability in a sulfuric environment.

Enhanced Electrochemical H2O2 Production via Two-Electron Oxygen Reduction Enabled by Surface-Derived Amorphous Oxygen-Deficient TiO2–x

“…Such a clear peak shift toward a high frequency is attributed to the increase of oxygen vacancy in the prepared a-TiO 2– x /TiC catalyst . Electron paramagnetic resonance (EPR) spectrum of a-TiO 2– x /TiC (Figure f) shows a typical signal ( g = 2.002) for unpaired electrons trapped by the oxygen vacancies of a-TiO 2– x , − which can be attributed to the fact that the acid treatment causes surface oxidation of TiC to form a highly disordered layer, resulting in the increased signal intensity of oxygen vacancies . Together with these analyses, it is safe to conclude that TiC experienced strong surface oxidization to generate amorphous oxygen-deficient TiO 2– x during concentrated sulfuric acid treatment in the present study.…”

Prevention of Carbon Corrosion by TiC Formation on Ti Current Collector in Seawater Batteries

“…[ 30 ] As one can infer from the scanning electron microscope (SEM) images (Figure S2, Supporting Information), real contact between the carbon current collector and Ti is insufficient (which can be attributed to the smooth nature of Ti surfaces), resulting in high contact resistance at the cathode current collectors of SWBs. According to previous reports, the contact resistance problem is severe between pristine Ti and carbon‐based fabrics, which hampers the movement of electrons; [ 31 ] however, to the best of our knowledge, the contact resistance problem has received less attention than the slow OER/ORR kinetics in carbon current collectors. Moreover, Ti acts as an electron pathway and does not supply OER/ORR active sites, resulting in reduced performance.…”

“…[32] Moreover, the electrical resistivity of TiC (25-52 µΩ cm) is comparable to that of pristine Ti, indicating that the formation of TiC on the Ti surface does not negatively affect the bulk electrical properties of Ti. [31] Previous studies report TiC as an efficient OER catalyst in the forms of nano-sheets, [33,34] and nanoparticles. [35] In terms of ORR, nanowire or nano-dendrite forms of TiC are reported to exhibit better activity compared to bulk TiC, [36] where polar-TiC (111) facets are reported to be much more ORR active than non-polar-TiC (002) facets.…”

Effect of TiN Particle Size and Impurities on the Contact Resistance of TiN-Powder-Decorated Stainless-Steel Separator Electrodes for Fuel Cells

“…The electrical resistivity of TiN and TiC is 25 to 52 µ³•cm, and the electrical resistivity of TiO is 281 µ³•cm. 22,23) It is considered that the lower the content of impurities such as TiC and TiO, the closer to the value of TiN, which has a low electrical resistivity.…”